Process of preparing an organopolysiloxane, the product thereof, mixtures of the product with rubbery polymers, and method of curing the mixtures



limited States Patent PROCESS OF PREPARING AN ORGANOPOLY- SILOXANE, THEPRODUCT THEREOF, MIX- TURES OF THE PRODUCT WITH RUBBERY POLYMERS, ANDMETHOD OF CURING THE MIXTURES Dallas T. Hurd, Cleveland, Ohio, assignorto General Electric Company, a corporation of New York No Drawing.Application March 9, 1956 Serial No. 570,421

13 Claims. (Cl. 260-4) with (B) a controlled amount of vinyltrifunctional silicon compound having the following formula (2) FcH nR'n to produce a vinyl-containing organopolysiloxane gum which iscapable of being covulcanized with a natural or synthetic rubber toproduce a vulcanized elastomer. This invention also relates to theproducts so produced. In Formulas l and 2 m is an integer of at least 3,R represents members selected from the class consisting of alkylradicals, cycloalkyl radicals, aryl radicals, aralkyl radicals, haloarylradicals, etc. and mixtures of the aforesaid members, at least 50 molepercent of said members being methyl radicals, and R is alkyl, e. g.methyl, ethyl, propyl, butyl, pentyl, etc.

Heretofore, organopolysiloxanes have been incorporated in natural orsynthetic latices, gums or rubbers to enhance their properties. Althoughthe products so prepared are satisfactory in many applications, theysuifer the disadvantage of being mere mixtures of organopolysiloxaneswith rubber materials. Being mere mixtures, they tend to separate fromeach other during storage and use. Thus, when mixtures ofdimethylpolysiloxanes and natural or synthetic rubbers are stored, it isfound that there is a tendency for the siliconematerial to bleed out ofthe rubber base so that an intimate mixture is no longer present. Thissame bleeding eitect is also noticed when mixtures ofdimethylpolysiloxane materials and these rubbers are maintained atelevated temperatures. The net elfect of this bleeding is to decreasethe low temperature flexibility, decrease the thermal stability,decrease the effective strength, and decrease the moisture resistance ofthe mixtures. This bleeding defect of rubber has been eliminated byforming true covulcanizates of the silicone material with the rubber.Thus, vinyl-containing organopolysiloxane gums have been covulcanizedwith wellknown natural and synthetic gums to form covulcanizates of thesilicone gum and these gums. These covulcanizates display no bleeding,have improved moisture resistance over prior art materials includingstraight natural or synthetic rubbers, have higher temperature stabilitythan natural or synthetic rubbers, display greater flexibility at "icelow temperature than natural or synthetic rubbers, have improvedelectrical properties, and are more adaptable to commercial applicationsthan pure silicone rubbers since they are less expensive than siliconematerials due to the incorporation of less expensive natural orsynthetic rubbers.

Heretofore, it was believed that in order to prepare vinyl-containingorganopolysiloxane gums suitable for good covulcanizates with natural orsynthetic rubbers, it was necessary to use vinyl-containing difunctionalsilicon compounds since vinyl trifunctional silicon compounds tended toproduce prematurely cross-linked organopolysiloxanes which whencovulcanized would produce an inferior elastomer. Thus, in applicationSerial No. 450,230, I-lurd et al., filed August 16, 1954, and assignedto the same assignee as the present application, it was disclosed thatvinyl-containing organopolysiloxane gums suitable for covulcanizatescould be prepared from compounds such as the completely condensed cyclicvinyl-containing difunctional siloxanes which are themselves prepared byseparation from the hydrolysate of vinyl-containing difunctional siliconcompounds, for example, methylvinyldichlorosilane, methylvinyldiethoxy,divinyldichloro silane, divinyldiethoxysilane, etc. Although thecompositions discolsed in the above applicaton possess excellentproperties, they are relatively expensive since they are prepared fromthese relatively expensive difunctional vinyl silicon compounds.

Unexpectedly, l have now discovered a method of preparing vinylorganopolysiloxanes capable of being covulcanized with a natural orsynthetic rubber to produce a vulcanized elastomer which comprisestreating a mixture of (A) a substantially difunctional saturatedorganosilicon compound within the scope of Formula 1 and (B) 01-10%,based on weight of Formula 1 of a relatively inexpensive vinyltrifunctional silicon compounds within the scope of Formula 2. Moreparticularly, this reaction is carried out by (A) admixing compoundswithin the scope of Formulas l and 2, (B) catalytically rearranging andcondensing said mixture, and (C) thereupon hydrolyzing the alkoxy groupscontained therein.

I have also discovered that these new vinyl-containingorganopolysiloxane gums can be vulcanized with any of the well-knownnatural or synthetic gums. These covulcanizates display no bleeding,have improved moisture resistance over prior art materials, including,straight natural or synthetic rubbers, have higher temperature stabilitythan natural or synthetic rubbers, display greater flexibility at lowtemperature than natural or synthetic rubbers, have greatly improvedelectrical properties, and are more adaptable to commercial applicationswhere a less expensive el'a'storner is required than the siliconenatural or synthetic covulcanizates heretofore disclosed since thetrifunctional vinyl components containedftherein is less expensive thanthe difunctional vinyl components heretofore employed. p

A typical example of a mixture of a cyclic low molecular weightorganopolysiloxane and a vinyl trifunctional compound which can betreated according to this invention is a mixture ofoctamethylcyclotetrasiloxane and vinyltriethoxysilane. After mixingthese two compounds they are rearranged and condensed to a gum byeffecting reaction with a suitable organopolysiloxane rearrangement andcondensation catalyst. Thereupon, any ethoxy groups remaining in themixture are hydrolyzed with at least a stoichiometric amount of water.Excess water is advantageously used to compensate for some water whichis lost by vaporization. Hydrolysis is indicated by the evolution ofethyl alcohol. The gum so produced is then covulcanized with a naturalor synthetic rubber.

The. low molecular weight organopolysiloxane containmg only saturatedhydrocarbon radicals bonded to silicon with which the vinyltrifunctional silicon compound is copolymerized may be one or more ofthe cyclic organopolysiloxanes described in Formula 1, where m is aninteger from 3 to or more and R represents members selected from theclass consisting of alkyl radicals, e. g., methyl, ethyl, propyl, butyl,octyl, decyl, etc. radicals; cycloalkyl radicals, e. g., cyclohexyl,cycloheptyl, etc.; aryl radicals, e. g., phenyl, diphenyl, naphthyl,etc.; tolyl, xylyl, etc.; aralkyl radicals, e. g., benzyl, phenylethyl,etc.; haloaryl radicals, e. g., chlorophenyl, dibromophenyl, etc.; andmixtures of the aforesaid radiols. At least 50 mole percent of the Rs ofFormula 1 should be methyl. Typical compounds within the scope ofFormula 1 include, for example, octamethylcyclotetrasiloxane,tetramethyltetraethylcyclotetrasiloxane, octaphenylcyclotetrasiloxane,etc. Methods of preparing these cyclic low molecular Weightorganopolysiloxanes particularly octamethylcyclotetrasiloxane aredescribed by Rochow in Chemistry of Silicones, 2nd ed., John Wiley &Sons (1951), pp. 79-81.

The trifunctional vinyl silanes within the scope of Formula 2 employedin this invention may be prepared by the methods disclosed in theabove-named Rochow text, pp. 55-56. These trifunctional vinyl silanes,although relatively inexpensive, have not found wide usage in gumsbecause their cross-linking power is more adaptable to solid resins thanto elastomers.

A critical feature of this invention is the amount of trifunctionalvinyl silanes that can be incorporated into the gum without destroyingits utility as a covulcanizate. Thus, the amount of trifunctional vinylsilanes that can be incorporated into the gum is 0.1% to 10% andpreferably 2 to 8%, based on weight of the difunctional saturatedorganosilicon compound. As of present knowledge, it is not understoodwhy these percentages of trifunctional vinyl compounds can be used,sincewhen larger amounts are used, there is a great tendency to formsiloxane cross-links.

These mixtures of compounds within Formulas 1 and 2 can be copolymerizedwith known organopolysiloxane rearrangement and condensation catalysts.Thus, they can be copolymerized to gums readily by using from about0.001 to 0.5 percent by weight of strong bases such as those describedin U. S. Patents 2,443,353, 2,634,252, etc. for example, potassiumhydroxide, cesium hydroxide, rubidium hydroxide, etc. at elevatedtemperatures of the order of from about 110 to 150 C. in times rangingfrom about 10 to 30 minutes. In general, copolymerization of thesemixtures is effected by heating to a temperature of about 110 to 150 C.and then adding the desired organopolysiloxane rearrangement and condensation catalyst. However, if desired, the catalyst may be added priorto heating of the mixture to cause polymerization to a gum to beeffected when the mixture is later heated to temperatures of the orderof 110 to 150 C.

Thereupon water is added to the reaction mixture at a temperature highenough to hydrolyze any alkoxy groups present in the mixture. Since itis desirable to remove alcohol or any excess water from the reactionmixture, the addition is usually carried out above 100 C. Afterhydrolysis is complete the vinyl gum should not be heated at elevatedtemperatures for long periods of time. Thus, in the case of thevinyltriethoxysilane, the gum formed therefrom should be cooled to roomtemperature after the ethoxy groups are hydrolyzed and the alcoholformed thereby is removed from the gum.

The natural or synthetic gums employed in the covulcanizatc of thepresent invention may he the natural gum from which natural rubbers areprepared or any of the well-known synthetic gums from which thesynthetic rubbers are prepared. The term gum as used in the presentapplication is intended to mean the solid,

rubbery polymer, copolymer or interpolymer from which vulcanized rubbersare prepared as distinguished from the vulcanized rubber itself. Amongthe synthetic gums which may be employed in the practice of the presentinvention are, for example, butyl gum, styrenebutadiene gum, nitrilegum, neoprene gum, polyacrylic ester gum, polysulfide gum, isobutylenegum, etc. The term butyl gum is intended to mean, broadly, a solidrubbery copolymer or interpolymer comprising the product ofpolymerization of a mass of copolymerizable materials containing byweight a major proportion of a low molecular weight olefin (monoolefin),more particularly, an isoolefin, e. g., isobutylene (isobutene),2-ethylbutene-1, etc., and a minor proportion of a low molecular weightconjugated diolefin, e. g., butadiene, isoprene, cyclopentadiene,pentadiene-1,3, hexadiene-2,4, etc. More specific examples of butyl gumsembraced by the above definition are those wherein the amount ofdiolefin present is from about 2 to 5 percent, by weight, of the totalweight of the monoolefin and the diolefin. This butyl gum is availableto the trade and is also known as GR-I. Reference is made to Thomas etal., U. S. Patent 2,356,128, issued August 22, 1944, for more detailedinformation concerning butyl gum, its properties-and method ofpreparation. Typical of the compositions disclosed by Thomas et al. is asynthetic solid, plastic hydrocarbon interpolymer of a major proportionof an isoolefin having less than 8 carbon atoms per molecule and a minorproportion of a conjugated diolefin having from 4 to 8, inclusive,carbon atoms per molecule, which interpolymer is characterized by lowsaturation as evidenced by an iodine number below 50, a molecular weightabout 15,000, and an approximate specific gravity of 0.91. Butyl gumalso includes copolymers of isobutylene and small amounts of isoprene aswell as those copolymers wherein butadiene, dimethylbutadiene, orpiperylene is substituted for isoprene in the isobutylene copolymer.

Styrene-butadiene gum, commonly referred to as GR-S or styrene gum is acopolymer of approximately 70 to percent of butadiene and 20 to 30percent of styrene. Nitrile gum, commonly known as Buna N, refers to acopolymer of butadiene and acrylonitrile containing from about 55 to 80percent butadiene and 20 to 45 percent, by weight, of acrylonitrile.Neoprene gum is a high molecular weight polymer of chloroprene(Z-chlorobutadiene). The polyacrylic ester gums are high molecularWeight condensation products of acrylic acids and alcohols such asn-butanol. Polysulfide gums are the rubbery condensation products of anorganic dihalide and an alkaline polysulfide. Isobutylene gum is thehigh molecular weight homopolymer of isobutylene. For a more completediscussion of the compositions, properties, and preparation of thesynthetic gums within the scope of the present invention, attention isdirected to Modern Syn thetic Rubbers, by Harry Barron, published in1944 by D. Van Nostrand (30., New York, N. Y.; Vinyl and RelatedPolymers, by Calvin E. Schildknecht, published in 1952 by John Wiley &Sons, Inc., New York, N. Y.; and to Synthetic Rubber, by G. S. Whitby,published in 1954 by John Wiley & Sons, Inc., New York, N. Y.

The covulcanizable mixture of the vinyl-containing organopolysiloxaneand the natural or synthetic gum may be vulcanized in the same manner asa percent natural or synthetic gum is vulcanized. sulfur vulcanizationagents including sulfur, sulfur halides, or sulfides may be used toeffect vulcanization. The vulcanizable material may also contain any ofthe various reinforcing fillers such as carbon black, zinc oxide, clay,whiting, slate flour, silica, etc., incorporated into the covulcanizablemixture. Preferably, I employ carbon black as a filler for thecovulcanizable material of the present invention since carbon blackappears to be the most effective reinforcing agent and is relativelyinexpensive. As in the case of 100 percent natural or synthetic rubbers,the covulca'nizate of the present invention Thus, typical "5 may haveincorporated therein cure accelerators suchas mercaptobenzothiazole,diphenylguanidine, tetramethylthiuramdisulfide, zinc.dimethyldithiocarbamate, benzothiazodisulfide, etc. The covulcanizatealso may have incorporated therein accelerator activators such as zincoxide, stearic acid, etc., as well as softeners, odorants, and pigments.In general, the formulation for the covulcanizate of the presentinvention comprises (A) from 45 to 99 percent, by weight, of a mixtureof from 25 to i 95 percent natural or synthetic gum and 5 to 75 percent,by weight, of a vinyl-containing organopolysiloxane guru which isprepared from a mixture of the compounds coming within the scope ofFormulas 1, and 2, (B) from to 50 percent, by weight, of filler, and (C)from 1 to percent, by weight, of a sulfur curing agent. Where anaccelerator is employed, I employ from about 0.5 to 5 percent of theaccelerator, based on the total weight of the covulcanizate, and fromabout 0.5 to 5 percent, by weight, of an accelerator activator, based onthe weight of the covulcanizate.

The covulcanizable materials of the present. invention may be preparedby thoroughly mixing the natural or synthetic gum with thevinyl-containing organopolysiloxane gum on a differential rubber millingroll or in a Banbury mixer. The two ingredients are milled with therequired amount of the sulfur vulcanization agent until a completelyuniform mixture is obtained. Where the covulcanizate has a filler and anaccelerator and an accelerator activator incorporated therein, theingredients are milled in a similar manner on rubber diflerential rollsor in a Banbury mixer until a uniform mixture is obtained. After millingof the covulcanizable mixture is effected, vulcanization is effected byheating the mixture at temperatures from about 110 to 160 C. untilvulcanization is completed. This heating operation may take place in anoven at atmospheric pressure, or in a heated press, or on heated rollsor in an extrusion apparatus. The time required for vulcanization variesfrom a few minutes to several hours depending on the particularmaterials employed and whether or not a vulcanization accelerator isemployed.

The following examples are illustrative of the practice of our inventionand are not intended for purposes of limitation. All parts are byweight.

Example 1 A mixture of 100 parts of octamethylcyclotetrasiloxane and 4parts of vinyltriethoxysilane was heated to 150 C. whereupon 0.1 part ofcesium hydroxide was added. Within about ten minutes, the siloxane hadpolymerized to a syrup and it appeared that polymerization would proceedno further. At this point while the temperature was about 150 C.sufficient water was added dropwise to hydrolyze the ethoxy groups asthe reaction was vigorously stirred. This required somewhat more thanthe stoichiometric quantity owing to some loss of water byvolatilizatio-n from the hot mixture. Copious quantities of ethylalcohol vapor were released from the mixture during this hydrolysis, andwhen the evolution of alcohol ceased, the addition of water was stopped.Within a few minutes the material had polymerized to a gum which wasthen allowed to cool to room temperature.

Example 2 One hundred parts of the gum prepared in Example 1 were milledwith 100 parts of butyl rubber gum (a copolymer of diolefin and a majorproportion of isobutylene, namely, 2 parts by weight of isoprene and 98parts by weight of isobutylene). To this thoroughly mixed blend wereadded 100 parts of carbon black filler (Kosmos 60), 3 parts of sulfurtogether with 1 part of an accelerator (benzothiazyl disulfide,(C6H4;NCS)2S2, and 1 part of zinc oxide. The resulting milled productwas press-cured for hour at 150 C. and then further cured in an oven for1 hour at 150 C.

The elastomer so produced appeared to be a true covulcanizate since itexhibited no bleeding" of the sili cone phase after several days at roomtemperature. The elastomer had a room temperature tensile strength of850 p. s. i. and was flexible at a temperature as low as 30 C.

Example 3 imilar covulcanizates are also prepared in the manner ofExample 2 except that other natural or synthetic rubbers are substitutedfor the butyl gum. Covulcanizates are prepared with (l) a milled palenatural crepe gum, (2) a nitrile gum (a copolymer of approximately 65percent butadiene and 35 percent acrylontrile), and (3) GR$ gum (acopolymer of 76.5 percent of butadiene and 23.5 percent of styrene).

Although the foregoing examples describe covulcanizable mixtures ofvarious natural or synthetic gums and a specific vinyl-containingorganopolysiloxane gum, it should be understood that other natural. orsynthetic rubbers (e. g. other natural rubber gums, other butyl gums,other nitrile gums, neoprene gums, polyacrylic ester gums, polysulfidegums, isobutylene gums, or any of those gums heretofore described), andother organopolysiloxane gums containing other saturated groups (e. g.as ethyl, phenyl, cyclohexyl, etc.), and unsaturated groups (e. g.allyl, substituted allyl such as methallyl, etc.) may be used in placeof, or in addition to, these ingredients disclosed in the examples.Although the examples disclose only covulcanizates containing fillers,it should be understood that the mixtures of the present invention maybe cured by sulfur without the addition of any filler.

The covulcanizable mixtures of the present invention are useful per seas a dielectric material in transformers, capacitors and the like whereextremes of temperatures are encountered and are useful per se asintermediates in the preparation of covulcanized rubbery products. Thesecovulcanized rubbery products, whether containing fillers or not, arevaluable as gasket material, wire coating material, as fillers forelectrical cables, as encasing materials for transformers, capacitors,and the like where extreme resistance to changes in temperatures isdesired along with high dielectric strength, moisture resistance, andrelatively low cost, and for other application, such as aircraft tires,rubber tires or structural parts for automotive vehicles, militaryequipment, etc. where improved flexibility and strength over a widerange of temperature is desired.

What I claim as new and desire to secure by Letters Patent of the UnitedStates is:

1. A process of preparing a vinyl-containing organopolysiloxane whichcomprises admixing (1) a cyclic organopolysiloxane of the formula [(R)SiOl and (2) 01-10%, based on the weight of (1), of an organosilane ofthe formula CH =CHSi(OR') where m is an integer and is at least 3; R isa member selected from the group consisting of alkyl, cycloall-tyl,aryl, aralkyl, and haloaryl radicals at least 50 mole percent of saidmembers being methyl radicals; and R is alkyl; reacting said mixture of(1) and (2) in the presence of a strong base and thereafter hydrolyzingthe resulting condensate.

2. The vinyl-containing organopolysiloxane produced by the method ofclaim 1.

3. A composition comprising (a) the product of claim 2 and (b) a memberselected from the group consisting of natural rubber, rubbery syntheticpolymers of a conjugated diene, rubbery polymers of acrylic acid esters,rubbery polysulfide polymers which are condensation products of anorganic dihalide and an alkaline polysulfade, and rubbery homopolymersof isobutylene.

4. The cured product obtained by heating the composition of claim 3 to atemperature in the range of to C. in the presence of a sulfurvulcanizing agent.

5. A composition comprising (a) the product of claim 2 and (12) naturalrubber.

2 and (b) a rubbery copolymer of isobutylene and a minor 5 proportion ofa conjugated diene.

8. The cured composition obtained by heating the product of claim 7 to atemperature in the range of 110 to 160 C. in the presence of a sulfurvulcanizing agent.

9. The composition comprising (a) the product of claim 2 and (b) arubbery copolymer of butadiene and styrene.

10. The cured composition obtained by heating the product of claim 9 toa temperature in the range of 110 to 160 C. in the presence of a sulfurvulcanizing agent.

11. The composition comprising (a) the product of claim 2 and (b) arubbery copolymer of butadiene and acrylonitrile.

12. The cured composition obtained by heating the product of claim 11 toa temperature in the range of 110 to 160 C. in the presence of a sulfurvulcanizing agent.

13. A method of curing a composition comprising (a) the product of claim2 and (b) a member selected from the group consisting of natural rubber,rubbery synthetic polymers of a conjugated dieue, rubbery polymers ofacrylic acid esters, rubbery polysulfide polymers which are condensationproducts of an organic dihalidc and an alkaline polysulfide, and rubberyhomopolymers of isobutylene, and (c) 1 to 5% sulfur, based on the totalweight of the composition, which comprises heating said blend of (a),(b), and (c) to a temperature in the range of 110 to 160 C.

References Cited in the file of this patent UNITED STATES PATENTS2,445,794 Marsden July 27, 1948 2,589,317 Young et al Mar. 18, 19522,737,506 l-Iurd et al. Mar. 6, 1956 OTHER REFERENCES Kant-or et 211.:four. Am. Chen1.'Soc., 77 (1955), 1685- 1687.

Hauser: Rubber Age, April 1955, pages 73-76.

Mark et al.: Collected Papers of Wallace H. Cal-0thers, pages 391, 392,published 1940, Inter-science, N. Y.

1. A PROCESS OF PREPARING A VINYL-CONTAINING ORGANOPOLYSILOXANE WHICHCOMPRISES ADMIXING (1) A CYCLIC ORGANOPOLYSILOXANE OF THE FORMULA((R)2SIO)M AND (2) 0.1-10%, BASED ON THE WEIGHT OF (1), OF ANORGANOSILANE OF THE FORMULA CH2=CHSI(OR'')3 WHERE M IS AN INTEGER AND ISAT LEAST 3; R IS A MEMBER SELECTED FROM THE GROUP CONSISTING OF ALKYL,CYCLOALKYL, ARYL, ARALKYL, AND HALOARYL RADICALS AT LEAST 50 MOLEPERCENT OF SAID MEMBERS BEING METHYL RADICALS; AND R'' IS ALKYL;REACTING SAID MIXTURE OF (1) AND (2) IN THE PRESENCE OF A STRONG BASEAND THEREAFTER HYDROLYZING THE RESULTING CONDENSATE.